With the recent accelerated reduction in the size and weight of mobile information terminals such as cellar phones, notebook computers, and smartphones, secondary batteries serving as driving power supplies have been required to have a higher capacity. Nonaqueous electrolyte secondary batteries, which are charged and discharged by the movement of lithium ions between positive and negative electrodes, have a high energy density and a high capacity and therefore are widely used as driving power supplies for the above mobile information terminals.
Furthermore, nonaqueous electrolyte secondary batteries have recently attracted attention as power supplies for driving, for example, power tools, electric vehicles (EVs), and hybrid electric vehicles (HEVs, PHEVs) and are promising for various uses. Such power supplies for driving are required to have a higher capacity that allows long-term operation and improved output characteristics in the case where charge and discharge are repeatedly performed with a large current within a relatively short time.
In particular, when nonaqueous electrolyte secondary batteries are used as power tools, EVs, HEVs, PHEVs, and the like, a higher capacity needs to be achieved while output characteristics during charge and discharge with a large current are maintained.
For example, PTL 1 discloses that gas generation inside a battery during storage can be suppressed by coating a composite oxide mainly made of lithium nickelate with a tungstate compound and a phosphate compound and performing heat treatment.